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Technical
Printing Tips
- In one of the drawings you will see all parts in ready to print position
- You will need a few little supports for the Main Bottom parts and for the Steering Axle, but you should be able to print the rest of them without supports
- Most of the parts must be printed with 0.4mm perimeter thickness, just the Plate is a 1mm shell and must be printed with 0.48mm perimeter thickness
- The overhang wall in Top parts should be perfectly done without supports
- The weight of all printed parts should be around 170g of PLA with 2 perimeters, 5/5 Top/Bottom and 15% infill
- Clean up the holes with a 3mm philips screw driver or with an x-acto knife, I use the first method
- Try to print specially accurately the Steering Springs and the Throttle Levers, Trigger and Trigger Top
- Try to have a very good inter-layer adhesion to avoid tall thin parts breaking while assembling
Assembly order
- 1º I would suggest you to start printing the Main Rear parts. You can join them with two M3x8mm Shocket-Head screws
- 2º Introduce your Arduino and your antenna with the cables in a position than the cables doesn't disturb too much and the arduino mostly stays in place
- 3º Connect Female-Female Dupont cables to A0 and A1 in the Arduino
- 4º Introduce the "Octopus" with five GND/5V pairs made with female dupont cables. Two of the pairs should be longer, to reach the control plate and the steering wheel
- 5aº Time to prepare the Throttle Assembly. Take the Throttle Base and fix the potentiometer to it. Find a near center point of the pot and introduce the Trigger oriented in its final central position
- 5bº Introduce the throttle parts in the right order and position, use the drawing as a guide. Use one M3x8 screw to finally secure the parts in the trigger and finally use two M3x16 to fix the bearing holder
- 5cº Connect the A0, 5V and GND to the Throttle Potentiometer and bring the Throttle Assembly to its place. Use two M3x10 screws near the trigger and one M3x12-16 in the other hole
- 6º With Antenna and Throttle Pot connected to the arduino, connect it by USB to see if things are working at this step, maybe use Serial Port Viewer in arduino IDE connected to the receiver
- 7º Screw the Front Bottom part with one M3x16 to the Rear Bottom. Also use one of the two M3x25 screws to place Battery Door. You should be able to open it, don't screw too much
- 8º Add battery spring connected to the positive plate in the Battery Door... I hope the measures of what you have are similar to mines... If they aren't you will need to do some magic
- 9º Add battery spring and positive plate to the place for it inside Main Rear Top. Connect the spring (GND of battery) to the GND near the Vin pin using F-F dupont cable or some magic
- 10º If you have a power button in the Control Plate, connect the positive plate from the battery to the button, and the button to the Vin pin in the Arduino, magic needed here probably ;)
- 11º Time to test the battery connection. Use your power button or close the battery door to see if your arduino starts working. Success?¿?
- 12aº Mount Steering Base under Main Front Top and screw it from the outside using two M3x8 screws. Install the pot there, then the springs and finally the Axle12mmHEX part
- 12bº Wire the steering potentiometer to GND, 5V and A1 pin in the arduino. Make some tests connecting the arduino by USB or switching it ON with your battery and check in the receiver
- 13º If you have to wire some pots / switches in the control plate it is time to do it... Then aproximate Main Front Top part. The hardest part will be making the arduino take its final place.
- 14º If you could close it, it is time to screw! Use two M3x8mm to screw the Main Front Bottom to Main Front Top. Use two M3x16mm to screw Main Front Top to Main Rear Top
- 15º You have it! Just screw the external Antenna if you didn't before, add the car wheel to the Steering axle and screw it with a M3x8mm screw. Let's start calibrating your Radio :)
CALIBRATING THE RADIO
You will want to send a near 0 value when you go full-reverse, near 255 value when you full-throttle... The same way you will want to send a near 0 value when full steering left, and near 255 when full steering right.
Calibrating Throttle
The thing is that you are using just a range of your potentiometer bigger range. So you will be reading a value from the pot when the Throttle is in the center, I called that one in the firmware "Th_Center". Discover what's your Th_Center, but also your Th_Min and Th_Max values and introduce those data in the right place in the firmware. Play specially with those min and max values and re-upload firmware until you see you are "sending" the right values when you full-throttle or full-reverse, remember, near 255 and near 0
The next idea, to avoid strange behavours in the car, is to have a constant 127 value (half of the 0-255 range) being sent from the radio when the Throttle trigger is idle. For that I developed the "Th_Dead", the dead-zone near the central position which will make the radio send 127 until you move the trigger beyound certain point from the central position. This is important, increase or decrease the percent value and take a deep look to the code to understand it fully. I'm not using Th_Trim finally as I think can interfere with this code
Finally maybe you want to "cap" the forward or the reverse max speed... look for Th_FWD_Cap and Th_RWD_Cap values and change them between the limits to your likes. Remember that some RC Car ESCs will need you to fully brake before letting you using reverse... You won't be able to reverse if you cap the RWD direction so much. The same way you are capping the brake force too so be careful
Calibrating the Steering
Find your St_Min and St_Max values un-commenting the right line of the code. Introduce those values in the right place in the firmware, re-upload and lets see how far from the center (127 value) the center position is... The steering system can be inproved, is not as accurate now as the throttle one... So it will probably idle around a range... Use Th_Trim, negative or positive, to correct that middle value until the center of the range is around 127. If you have your Th_Trim "Wired" to a pot, just use the pot to find that spot.
The same I did with the Th_Dead could be done with something like St_Dead... If you review carefully the code, you should be able to implement it relatively easy, will you?¿? ;)
WHAT MORE COULD YOU DO WITH THE SYSTEM
If you take a look to the web, there are many things than can be incorporated both to the tx and the rx...
- You could use maybe an accelerometer in the radio to control other 2 channels
- Add a lot of push buttons to command some channels or params
- Add a little screen and show up there some values
- Measure battery voltage and trigger an alarm for low voltage
- Add a Buzzer in the radio for audible signals
- Replace 6xAA for a 18650 LiPo cell and a boost up module
- Add an accelerometer (gyro) in the car and program it to drift!
- Receive alarm in radio about low voltage in vehicle, or show the car or radio cell voltages in screen
- Add a front distance sensor to try to avoid front impacts
As you can see, those are just a bunch of ideas, but you could come up with many better ones! I hope you want to give it a try and tell us about it!
WHAT MORE COULD I DO?¿?
- I can design a different shell, maybe for a "more pro" radio, based on li-po, with usb charging, screen, speaker and maybe a menu interface for settings...
- I can work in the line of improving code for more secure RF communication, maybe a binding procedure, storing and reading values from eeprom...
- I can design a "drone" style radio, with two joysticks, many pots and switches and maybe space for a screen...
- I can try to design and code a RC Car light "smart" system for the arduino receiver...
- I can design an arduino based MyRCCar
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Hi there! I'm an individual who has been designing and playing with RC cars and Slot cars for some years. Take advantage downloading and playing with my designs :) Let your screen rest for a while building and playing physically!
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